AVS 49th International Symposium
    Nanotubes: Science and Applications Topical Conference Monday Sessions
       Session NT-MoA

Paper NT-MoA9
Comparing Light Gas Diffusion Rates in Carbon Nanotubes and Zeolites

Monday, November 4, 2002, 4:40 pm, Room C-209

Session: Nanotubes: Chemical Functionalization, Sensors
Presenter: A.I. Skoulidas, Carnegie Mellon University
Authors: A.I. Skoulidas, Carnegie Mellon University
D. Ackerman, University of Pittsburgh
J.K. Johnson, University of Pittsburgh
D.S. Sholl, Carnegie Mellon University
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As in all microporous materials, the diffusion rates of molecules adsorbed in carbon nanotubes may have a large impact on the feasible applications of these materials. We have used atomistic simulations to compare the diffusion rates of H@sub 2@ and CH@sub 4@ in a range of defect-free single-walled carbon nanotubes with two silica zeolites with similar pore sizes, silicalite and ZSM-12. One advantage of comparing our results with these two zeolites is that we can validate the accuracy of our simulations against a large body of experimental data. We have used equlilibrium Molecular Dynamics and Monte Carlo methods to determine both the self diffusivity and the transport diffusivity of H2 and CH4 adsorbed as single components in carbon nanotubes. The transport diffusivity is the relevant quantity for describing macroscopic mass transfer in applications such as reversible adsorption cycles and membranes. We find that diffusion in carbon nanotubes is orders of magnitude faster than in the two zeolites over a broad range of pressure and temperature. These diffusivities are in fact among the fastest known for light gases in any environment, including bulk gas phases. This dramatic result can be understood in terms of the smoothness of the potential energy surface created by carbon nanotubes. We will discuss the implications of our results for using carbon nanotubes for highly permeable membranes.